Though it seems unusual, feeding chicken poop to cows has actually been a practice for a long time, going back to the dawn of agriculture.

“In the old days when people had mixed farms, what came out the back end of the cows was eaten by pigs, and what came out the end of pigs was eaten by chickens. That was the natural way of farming,” said Dean Cliver, professor emeritus of food safety at UC Davis. “Anything that hit the ground was fair game.”

But that doesn’t necessarily mean that we should keep doing it, says the coalition of consumer groups fighting to ban the practice, which is arguing that feeding this so-called “poultry litter,” including feces, spilled chicken feed, feathers and poultry farm debris, increases the risk of cows becoming infected with mad cow disease.

That's because spilled chicken feed and feces can contain tissue from ruminants like cows and sheep. When cows eat other cows, the disease can be transmitted, as the public found out almost six years ago when the first U.S. case of mad cow disease was discovered.

"It takes a very small quantity of ruminant protein, even just 1 milligram, to cause an infection," said Steve Roach, public health program director with Food Animal Concerns Trust, a Chicago-based animal welfare group that is part of the coalition.

According to the FDA, farmers feed 1 million to 2 million tons of poultry litter to their cattle annually.

But this time it’s not just the consumer advocacy groups getting riled up. McDonald’s Corp., which happens to be the largest restaurant user of beef, also wants the FDA to prohibit the practice.

In a statement concerning the issue, the company said, "We do not condone the feeding of poultry litter to cattle.”

Though the statement itself is pretty mild, it's actually kind of a big deal considering that it came from the nation’s biggest fast-food giant. In other words, when McDonald's has something to say, people tend to listen.

For example, back in the late '90s, McDonald’s was able to get its egg suppliers to stop a practice known as force molting, which involves depriving food to hens near the end of their lives to trick their bodies into laying eggs one last time. This sudden move came after years of work by animal rights organizations trying to accomplish the same goal, to little or no avail.

As a result of McDonald's position, forced molting was sharply curtailed in the U.S.

Of course, the beef industry’s main trade group, the National Cattlemen’s Beef Association is fighting back, pointing to several FDA reviews that have found the chance that cows becoming infected with mad cow disease from eating chicken litter is remote.

"Science does not justify the ban, and the FDA has looked at this now many times," said Elizabeth Parker, chief veterinarian for the trade group.

But it doesn't look like the consumer coalition group will be backing down anytime soon. According to the article, if the FDA does not institute a ban within the next couple of months, members of the coalition will file a lawsuit or push for federal legislation establishing a ban.